1. Field of the Invention
The present disclosure relates to the field of patient or driver monitoring. More specifically, the invention relates to the acquisition and processing of a blink electromyogram (EMG).
2. Description of the Related Art
The onset and occurrence of drowsiness has been long a problem for drivers. Studies indicate that fatigue could be a significant factor in the 100,000 U.S. commercial/passenger vehicle crashes per year. For example, some estimate that fatigue is a factor in approximately fifteen percent of fatal large truck-related crashes. In a 2005 study conducted by the Insurance Institute of Highway Safety, forty two percent (42%) of large truck drivers drove while sleepy during the previous week before being surveyed.
To combat this problem, the automobile industry developed several technologies to attempt to detect errant driving behavior. For example, lane departure systems, such as that disclosed in U.S. Pat. No. 6,930,593, often include a camera mounted near the interior rear view mirror that views the road ahead and detects lane markings. When the system determines that the vehicle is drifting out of its lane, a warning buzzer sounds and an icon may flash on the instrument panel. Embodiments of these types of systems are found at least in various Infiniti M sedans and were in part developed by Valeo and Iteris. However, lane departure systems usually require minimum speeds and a view of well marked lane markings. These system often struggle on roads with worn paint and roads covered with dirt, snow, rain, or the like, or in actual storm or wind conditions. Moreover, such systems often confuse desired lane changes, inattentive driving, and drowsiness.
Other systems turn the camera on the driver. Originally, because image processing of the face was difficult, Carnegie Mellon researcher Richard Grace transmitted a wavelength of light to a driver's eye from the dashboard, and received the reflected light as disclosed in U.S. Pat. No. 6,082,858. Grace focused on monitoring the percentage of time a driver's eye is closed, or PERCLOS. The PERCLOS monitor alarms when it detects a PERCLOS pattern that Grace recognizes as being associated with a driver getting drowsy. However, such cameras include significant drawbacks of being unusable and/or inaccurate when a driver wears sunglasses, subject to significant errors, and subject to interference when objects are placed between the emitter or lens and the face of the driver.
In an attempt to correlate a physiologic signal with drowsiness, Ulrika Svensson explored the use of the electrooculogram (EOG) in her thesis at the University of Linkoping. In general, the EOG comprises a record of the standing voltage of the retina, the layers of cells at the back of the eye that conduct vision processing. The EOG is correlated with eyeball movement and obtained by electrodes placed on the skin above and below, or left and right of, the eye. In Svensson's drowsiness system, the use of two sensors complicate blink monitor processing through the addition of noise. Further, because Svensson employs primitive curve fit-, threshold-type algorithms for detection, the system has difficulty accommodating motion artifact or a large range of EOG morphologies.